diff --git a/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php b/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
index e8c1008c183..f2a3412c599 100644
--- a/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
+++ b/src/Analyser/ExprHandler/Helper/ConditionalExpressionHolderHelper.php
@@ -172,9 +172,15 @@ public function processBooleanConditionalTypes(Scope $scope, SpecifiedTypes $con
 				continue;
 			}
 
+			$scopeType = $scope->getType($expr);
+			$conditionType = TypeCombinator::intersect($scopeType, $type);
+			if ($scopeType->equals($conditionType)) {
+				continue;
+			}
+
 			$conditionExpressionTypes[$exprString] = ExpressionTypeHolder::createYes(
 				$expr,
-				TypeCombinator::intersect($scope->getType($expr), $type),
+				$conditionType,
 			);
 		}
 
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14878.php b/tests/PHPStan/Analyser/nsrt/bug-14878.php
new file mode 100644
index 00000000000..dab39e4e12a
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14878.php
@@ -0,0 +1,89 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14878;
+
+use function PHPStan\Testing\assertType;
+
+// The `$b === true` and `$b === true && $cond` statements inside the branches
+// are what regressed: with the bug $b was narrowed to `mixed~true`, so they
+// emitted "Strict comparison ... will always evaluate to false" and "Result of
+// && is always false". They are referenced from BooleanAndConstantConditionRuleTest
+// and StrictComparisonOfDifferentTypesRuleTest as a regression guard.
+
+function test($a, $b, $cond): void
+{
+	if (
+		in_array($a, [1, 2])
+		&& $b === true)
+	{
+
+	} elseif (
+		$a == 3) {
+		assertType('mixed', $b);
+
+		$b === true;
+		$result = $b === true && $cond;
+	}
+}
+
+function testStrictElseIf($a, $b, $cond): void
+{
+	if (
+		in_array($a, [1, 2])
+		&& $b === true)
+	{
+
+	} elseif (
+		$a === 3) {
+		assertType('mixed', $b);
+
+		$b === true;
+		$result = $b === true && $cond;
+	}
+}
+
+function testPlainElse($a, $b, $cond): void
+{
+	if (
+		in_array($a, [1, 2])
+		&& $b === true)
+	{
+
+	} else {
+		assertType('mixed', $b);
+
+		$b === true;
+		$result = $b === true && $cond;
+	}
+}
+
+// Same degenerate-condition pattern without in_array: a loose `==` whose
+// falsey narrowing of $a is a no-op on a `mixed` type.
+function testLooseEqual($a, $b, $cond): void
+{
+	if (
+		($a == 1 || $a == 2)
+		&& $b === true)
+	{
+
+	} elseif ($a == 3) {
+		assertType('mixed', $b);
+
+		$b === true;
+		$result = $b === true && $cond;
+	}
+}
+
+// A genuinely conditional holder must still fire: $a === 1 makes the strict
+// in_array() antecedent true, so $b === true must have been false.
+function testMeaningfulHolderStillFires($a, $b): void
+{
+	if (
+		in_array($a, [1, 2], true)
+		&& $b === true)
+	{
+
+	} elseif ($a === 1) {
+		assertType('mixed~true', $b);
+	}
+}
diff --git a/tests/PHPStan/Rules/Comparison/BooleanAndConstantConditionRuleTest.php b/tests/PHPStan/Rules/Comparison/BooleanAndConstantConditionRuleTest.php
index 77e727ecb5d..fea58e7d61d 100644
--- a/tests/PHPStan/Rules/Comparison/BooleanAndConstantConditionRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/BooleanAndConstantConditionRuleTest.php
@@ -484,6 +484,12 @@ public function testBug14807(): void
 		$this->analyse([__DIR__ . '/data/bug-14807.php'], []);
 	}
 
+	public function testBug14878(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-14878.php'], []);
+	}
+
 	public function testInTrait(): void
 	{
 		$this->treatPhpDocTypesAsCertain = true;
diff --git a/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php b/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
index fc774b404e8..3da1fd10bed 100644
--- a/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/StrictComparisonOfDifferentTypesRuleTest.php
@@ -1244,6 +1244,11 @@ public function testBug14791(): void
 		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-14791.php'], []);
 	}
 
+	public function testBug14878(): void
+	{
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-14878.php'], []);
+	}
+
 	public function testBug14847(): void
 	{
 		$this->analyse([__DIR__ . '/data/bug-14847.php'], [